The invention concerns a belt to be used in paper-machine wet-pressing, in particular with an extended pressing gap. The belt is provided with a smooth, liquid-impermeable coating on its back side.
A substantial part of the liquid still present in the paper web is forced out by the wet-presses of paper machines. Compression rollers are used for this purpose and jointly form a pressing gap, through which passes the web and a revolving felt cloth. Due to the pressure applied in the pressing gap, the liquid is forced from the web and into the felt cloth, from which it is then drained.
Recently, wet-presses with an extended gap, the so-called nip-presses, have been developed. The web is moved over a longer path and accordingly, is exposed for a correspondingly longer time to high press squeezing so that and hence the web leaves the wet press in a drier state. Such wet presses have been disclosed, for instance, in the German Auslegenschriften Nos. 23 38 414 and 24 13 280, in U.S. Pat. Nos. 3,808,092 and 3,970,515 and in German Auslegeschrift No. 29 35 630 and German Offenlegungsschrift No. 29 35 630. Two basically different designs have been developed in the prior art.
In one design, the webs and one or two felt cloths pass between two liquid-impermeable belts in the pressing gap. The pressing gap is defined by two compression chambers or rollers resting against the back sides of said belts. The compression rollers are hydraulically actuated so that they compress from both sides the belts, the webs and the felt cloths passing between them.
In the other design, the web is guided over a section of one or more compression rollers, with a pressure being applied across this section in the direction of the compression roller. This is implemented too by a hydraulically actuated compression chamber acting on a flexible, liquid-impermeable belt revolving jointly with the web and the felt cloth.
The belts used for the above cited purposes are flexible plastic belts smooth on both sides. The plastic is resistant to the liquid used in the compression chambers and has high abrasion resistance. These belts cannot absorb the water forced from the web and therefore all of the water from the felt cloth(s) must be drained. Because of the high compression and the comparatively long compression path, the amount of water is larger than when wet-pressing without the extended pressing gap is utilized.